New South Wales in September 2017: driest on record with record-breaking heat

September 2017 in New South Wales was the State's driest start to spring on record. Rainfall was 86 per cent below average for the State, and the lowest on record for areas of the east coast and southwest. After some cold days at the start of the month, two blasts of warm air towards the end of September broke records for the warmest September day when averaged over the State, and highest temperature recorded anywhere in the New South Wales in September.

Driest September on record

Rainfall for New South Wales was 86 per cent below the monthly average, making it the driest September on record for the State

Much of the State away from the Alpine region and Upper Western District received less than 20 per cent of their average rainfall for September

Following on from a dry end to winter, the July to September period is now the second driest on record, with rainfall over the past three months 65 per cent below the average

New records set, and set again, for September heat

The average maximum temperature for the State was more than 2 °C above average, the sixth-warmest September on record

Minimum temperatures were slightly above average for the State as a whole (+0.29 °C), although below average in central and northeastern regions; several stations recorded their lowest September temperature on record on the 1st or 17th

The start of the month saw variable temperatures: many sites in the Central Tablelands and Central West Slopes and Plains districts had their warmest temperature ever recorded so early in the spring on the 3rd, while stations in the Southern Tablelands had their coldest September day since 2009 on the 5th

On the 23rd, warm air from central Australia moved across the State and set a new record for the warmest September day in New South Wales: the statewide mean maximum was 35.84 °C, more than 14 °C above average and a degree warmer than the previous record of 34.20 °C set on 22 September 2003

Over 99% per cent of the State experienced maximum temperatures in the top one per cent of observed September maximums, with more than half of the stations with at least 20 years of record reporting their warmest September day

Seven sites in New South Wales equalled or exceeded the previous State September maximum temperature record of 39.6 °C on the 23rd, with Wilcannia setting a new State record of 40.5 °C; before this month, no days above 40 °C had been recorded in September

These records were subsequently broken on the 27th by three stations as another pulse of heat crossed the State; Wanaaring set a new State record of 41.4 °C

Several stations with more than 50 years of data also reported their warmest September nights on record in the last week of the month, including Sydney's Observatory Hill, Coonabarabran and Newcastle

Notes

The Monthly climate summary,
generally published on the first working day of each month,
lists the main features of the weather in New South Wales using the most timely and accurate information available on the date of publication; it will generally not be updated. More extensive discussion of significant weather events, along with later information and data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review.

This statement has been prepared based on information available at
10 am on Monday 2 October 2017.
Some checks have been made on the data, but it is possible that results will change
as new information becomes available.

In some situations, some or all of the rainfall is in the form of hail or snow.
In these cases the totals given are for the water equivalent:
the depth of liquid water that results from melting any frozen precipitation.
There can be significant 'undercatch' of snow in strong winds,
meaning the true precipitation can be higher than that reported.

Averages for individual sites are long-term means based on observations from
all available years of record, which vary widely from site to site.
They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median
is sometimes more representative than the
mean
of long-term average rain.

The Rank indicates how rainfall this time compares with the climate record for the site,
based on the
decile ranking
(very low rainfall is in decile 1, low in decile 2 or 3,
average in decile 4 to 7, high in decile 8 or 9
and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a
percentage of the long-term mean.

Where temperature area averages are mentioned, they are derived from the
ACORN-SAT dataset.